Cities from Beijing to New Delhi are getting darker, glaciers in ranges like the Himalayas are melting faster and weather systems becoming more extreme, in part, due to the combined effects of man-made atmospheric brown clouds (ABCs) and greenhouse gases in the atmosphere.
These are among the conclusions of scientists led by Scripps Institution of Oceanography at UC San Diego climate and atmospheric sciences professor V. Ramanathan studying a more than three kilometer-thick layer of soot and other man-made particles that stretches from the Arabian Peninsula to China and the western Pacific Ocean.
Today the team, drawn from research centers in Asia including China and India, Europe and the United States, announced its latest and most detailed assessment of the phenomenon.
The brown clouds, the result of burning of fossil fuels and biomass, are in some cases and regions aggravating the impacts of greenhouse gas-induced climate change, says the report.
This is because ABCs lead to the formation of particles like black carbon and soot that absorb sunlight and heat the air, and gases such as ozone, which enhance the greenhouse effect of CO2.
Globally, however, brown clouds may be countering or masking the warming impacts of climate change by between 20 and up to 80 percent, the researchers suggest.
This is because of particles such as sulfates and some organics, which reflect sunlight and cool the surface.
The cloud is also having impacts on air quality and agriculture in Asia increasing risks to human health and food production for three billion people.
Achim Steiner, UN Under-Secretary General and Executive Director, UN Environment Programme (UNEP) said "one of UNEP's central mandates is science-based early warning of serious and significant environmental challenges. I expect the atmospheric brown cloud to be now firmly on the international community's radar as a result of today's report."
The phenomenon has been most intensively studied over Asia. This is in part because of the region's already highly variable climate including the formation of the annual monsoon, the fact that the region is undergoing massive growth and is home to around half the world's population.
But the scientists today made clear that there are also brown clouds elsewhere including over parts of North America, Europe, southern Africa and the Amazon Basin which also require urgent and detailed research.
"Combating rising CO2 levels and climate change is the challenge of this generation but it is also the best bet the world has for green growth including new jobs and new enterprises from a booming solar and wind industry to more fuel efficient, vehicles, homes and workplaces. Developed countries must not only act first but also assist developing economies with the finance and clean technology needed to green energy generation and economic growth," said Steiner.
"In doing so, they can not only lift the threat of climate change but also turn off the soot- stream that is feeding the formation of atmospheric brown clouds in many of the world's regions. This is because the source of greenhouse gases and soot are often one and the same - unsustainable burning of fossil fuels, inefficient combustion of biomass and deforestation," he added.
Ramanathan, head of the UNEP scientific panel which is carrying out the research said: "I would like to pay tribute to my distinguished colleagues, drawn from universities and research centers in Asia including China, India, Japan, Korea, Singapore and Thailand as well as Europe and the United States."
"Our preliminary assessment, published in 2002, triggered a great deal of awareness but also skepticism. That has often been the initial reaction to new, novel and far reaching, counter-intuitive scientific research," Ramanathan said.
"We believe today's report brings ever more clarity to the ABC phenomena and in doing so must trigger an international response - one that tackles the twin threats of greenhouse gases and brown clouds and the unsustainable development that underpins both," added Ramanathan.
"One of the most serious problems highlighted in the report is the documented retreat of the Hind Kush-Himalayan-Tibetan glaciers, which provide the head-waters for most Asian rivers, and thus have serious implications for the water and food security of Asia," he said.
"The new research, by identifying some of the causal factors, offers hope for taking actions to slow down this disturbing phenomenon; it should be cautioned that significant uncertainty remains in our understanding of the complexity of the regional effects of ABCs and more surprises may await us," added Ramanathan.
UN Environment Programme
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Scripps Institution of Oceanography at the University of California San Diego, is one of the oldest, largest, and most important centers for global science research and education in the world. Now in its second century of discovery, the scientific scope of the institution has grown to include biological, physical, chemical, geological, geophysical, and atmospheric studies of the earth as a system. Hundreds of research programs covering a wide range of scientific areas are under way today on every continent and in every ocean. The institution has a staff of more than 1,400 and annual expenditures of approximately $195 million from federal, state, and private sources. Scripps operates oceanographic research vessels recognized worldwide for their outstanding capabilities. Equipped with innovative instruments for ocean exploration, these ships constitute mobile laboratories and observatories that serve students and researchers from institutions throughout the world. Birch Aquarium at Scripps serves as the interpretive center of the institution and showcases Scripps research and a diverse array of marine life through exhibits and programming for more than 430,000 visitors each year. Learn more at scripps.ucsd.edu and follow us at Facebook, Twitter, and Instagram.
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